Trump says Singapore meeting was very interesting and that North Korea has great potential for the future.

United States President Donald Trump has said there is "no longer a Nuclear Threat from North Korea," on his return from a summit in Singapore with North Korean leader Kim Jong Un.

"Just landed - a long trip, but everybody can now feel much safer than the day I took office," he tweeted on Wednesday.

"There is no longer a Nuclear Threat from North Korea. Meeting with Kim Jong Un was an interesting and very positive experience. North Korea has great potential for the future!"

The summit was the first between a sitting US president and a North Korean leader and followed a flurry of North Korean nuclear and missile tests and angry exchanges between Trump and Kim last year that fuelled fears of war.

Independent experts say the North could have enough fissile material for anywhere between about a dozen and 60 nuclear bombs.

Last year it tested long-range missiles that could reach the US mainland, although it remains unclear if it has mastered the technology to deliver a nuclear warhead that could re-enter the atmosphere and hit its target.

And while Trump and Kim have signed a joint statement that contained a repeat of past promises to work toward a denuclearized Korean Peninsula, the details haven't been nailed down.

Trump has said strong verification would be included in a final agreement, with the particulars sorted out by his team with the North Koreans next week.

Trump's chest-thumping tweets seemed reminiscent of the "Mission Accomplished" banner flown behind President George W. Bush in 2003 when he spoke aboard a Navy ship following the US invasion of Iraq.

The words came back to haunt the administration, as the war dragged on throughout Bush's presidency.

When asked whether Trump was jumping the gun by declaring victory, White House counselor Kellyanne Conway told reporters: "This president wants North Korea to completely denuclearize so obviously that has to be complete, verifiable and irreversible. That will take a while."

Trump and Kim were returning to their respective strongholds following the talks - but to far different receptions.

In Pyongyang, North Korean state media heralded claims of a victorious meeting with the US president; photos of him standing side-by-side with Trump on the world stage were splashed across newspapers.

Trump, meanwhile, faced questions about whether he gave away too much in return for far too little when he bestowed a new legitimacy on Kim's rule and agreed, at Pyongyang's request, to end war games with Seoul that the allies had long portrayed as crucial to Asian safety.

'Joint military drills still necessary'

There were worries, especially in Tokyo and Seoul, which have huge US military presences, about Trump agreeing to halt US military exercises with South Korea, which the North has long claimed were invasion preparations.

That concession to Kim appeared to catch the Pentagon and officials in Seoul off guard, and some South Koreans were alarmed.

"The United States is our ally, so the joint military drills are still necessary to maintain our relationship with the US," said Lee Jae Sung, from Incheon.

"I think they will be continued for a while."

Secretary of State Mike Pompeo arrived at Osan Air Base south of Seoul from Singapore on Wednesday.

He met for nearly an hour at the air base with Gen. Vincent Brooks, commander of US Forces Korea, before heading by motorcade to Seoul.

Pompeo will meet President Moon Jae-in on Thursday morning to discuss the summit. Japanese Foreign Minister Taro Kono is also heading to Seoul and is due to meet with Pompeo and his South Korean counterpart.